Icing of aerodynamic surfaces is a well-known problem in the art of aeronautics. Icing can be partly mitigated by on-ground application of chemical compounds to prevent formation or adhesion of ice particles on the aerodynamic surfaces. However, with particular reference to open rotor aircraft propulsion systems, on-ground treatments have not proven generally effective for the duration of flight. Accordingly, various in-flight de-icing systems and methods have been used. For example, ice can be removed by microwave power impinging upon adsorbing structures on rotor blades to separate ice from the blade, as disclosed for example by U.S. Pat. Nos. 4,060,212 and 5,061,826. Equally, electrical heating elements can be mounted on rotor blades to separate ice from the blades, as disclosed for example by U.S. Pat. No. 5,131,812.
Known in-flight de-icing methods for propulsion rotors require transfer of power from the main airframe to the propulsion rotors. There are several difficulties with the various known methods for transferring power from the main airframe to the rotors of a contra-rotating open rotor aircraft propulsion system. Mechanical power transfer requires rotating contact between components that wear, bind, slip, and/or add undesirable weight and/or friction to the propulsion rotor assembly. Optical beam power transfer is susceptible to interference from opaque materials, and typically requires a fixed line-of-sight not easily achieved in a contra-rotating propulsion rotor system. Fluid power transfer along a contra-rotating propulsion rotor system requires provision of complex seals and fluid passages that are susceptible to wear and leakage. Radiative power transfer is difficult to focus, therefore prone to leakage that increases thermal management requirements of the propulsion system. Electrical power transfer, using slip ring assemblies, is a very common method that has proven failure modes associated with arcing caused by hydraulic fluid mixing with carbon dust formed by the slip ring brushes. Additionally, due primarily to brush wear, slip ring assemblies are high maintenance items requiring servicing on the order of hundreds of hours of operation. Within contra-rotating propulsion systems, the maintenance requirements associated with slip rings become both more frequent (because the contra-rotating elements rotate at higher relative speed, causing greater rates of brush wear) and more problematic (because at least one slip ring is “buried” within the contra-rotating shaft assembly). Moreover, in a typical contra-rotating propulsion system, one of the propulsion rotors is arranged distally from the main airframe. In such a typical contra-rotating propulsion system, electrical power can be provided from the main airframe to the distal propulsion rotor only through a sequence of two slip rings. Sequential arrangement of slip rings reduces the efficiency of power transfer, and also significantly worsens the chance of a failure in the overall electrical power transfer system.
With the foregoing problems and concerns in mind, it is the general object of the present invention to provide a system of power transfer, within a contra-rotating open rotor aircraft propulsion system, which overcomes the above-mentioned drawbacks.